Water heater having improved temperature control

ABSTRACT

A water heating system for a water heater includes a water tank and a heating element heating the water in the tank. A temperature controller has a temperature sensor and a temperature setting device that controls water temperature responsive to a user set temperature. A demand controller controls the temperature controller to override the set temperature responsive to demand for heated water. Demand is determined by water use measured by water flow. During non-demand periods the heating element can be turned off.

BACKGROUND

A water heater, such as a residential water heater, can have a water tank and a controller or thermostat where the user sets the relative operating temperature of the heater so that water of a desired temperature is produced by the heater. The settings can be vacation, warm (approx. 95 degrees F.), hot (approx. 105-110 degrees F.) and very hot (approx. 140 degrees F.). As the heater operates when the temperature of the water gets above the setting the heating controller turns off a heat source, such as an electric element for an electric water heater and a gas burner for a gas water heater. When the temperature falls below a lower offset temperature, the controller turns on the heat source. This control where the water temperature is kept at the desired temperature is performed continuously throughout each day.

During a typical day of hot water use there are times when there is little or no demand for hot water, such as when the residents are asleep or, if they work outside the home, when they are at work. What is needed is a hot water heater that will not heat the water when there is no demand.

DRAWINGS

FIGS. 1, 2, 3 and 4 depict an embodiment that turns on/off a heating controller.

FIGS. 1, 5, 6 and 7 depict an embodiment where a temperature setting controls the heating.

FIGS. 1, 5, 8 and 9 depict an embodiment with temperature control.

FIGS. 1, 5, 6 or 8 and 10 depict another embodiment having a start of heating control.

FIGS. 5, 6 or 8, 11, 12 and 13 depict an embodiment using water flow or hot water demand.

FIG. 14 shows a control process.

FIG. 15 shows a demand period.

FIG. 16 shows a two tank system.

FIG. 17 shows a temperature based learning process of anther embodiment.

DETAILED DESCRIPTION

As depicted in FIG. 1, a water heater 110 can include a tank 112, a temperature sensor 114, a temperature controller 116 that monitors the sensor for the current water temperature and sends a control signals to a heating controller 118 that controls the on/off of the heating element 120.

To allow control of the heating of the water relative to demand, a temperature storage 210, such as a RAM or PROM, is included, as depicted in FIG. 2. The temperature storage includes an on/off indicator 212 or bit for each period during a day, week, month, etc. during which temperature control is to be performed. FIG. 2 shows settings for a Saturday of a week and for the period from 9:30-10:45 in increments of ¼ hour. Each “0” indicator 212 indicates that during that period the heating unit 120 or element is to be turned off and each “1” indicates that during that period the heating unit 120 can be turned on and operated at the residents desired temperature setting with the offset using the typical control discussed previously.

To facilitate the indicator based control, as depicted in FIG. 3, an input unit 310, such as a display with a temperature set button, a number pad, day selector, etc. can be provided. The input unit 310 allows the user to set the time periods when the desired temperature water is to be provided. For example, the user can enter a start time of 8:15 and an end time of 9:30 as depicted in FIG. 2. A processor 312, such as a microcontroller, sets the indicator bits of the temperature storage to “1” for the periods between and inclusive of the start and end time. During operation the processor 312 monitors the current time by accessing a time clock of the system, accesses the storage 314/210 to obtain the indicator value and when the heating unit 120 is to be turned off, activates a relay 316, typically an electronic relay, that is closed when an open signal is not applied, to disconnect or interrupt the control signal from the temperature controller to the heat control by opening the relay. When the indicator is “1” the relay remains closed to allow the control signal to be sent from the temperature controller 318/116 to the heat controller 320/118.

An alternate operation approach as discussed in the embodiments is to load the temperature controller with a desired temperature as needed and allow it to control the heat controller as depicted by the dashed lines in FIG. 3.

FIG. 4 depicts an approach 410 to the process performed by the processor 312. When the input unit 310 is activated 412 by a user, such as the resident, the processor 312 determines 414 whether the user has activated the setting function. If so, the user is allowed to enter start times 416 and end times 418. When the no more start settings need to be made 420, the processor 312 sets 422 the temperature storage with the appropriate values for the indicator. When the operation is not in the setting mode, the processor 312 obtains 424 the current time and accesses 426 the temperature storage 314 of the corresponding time period. If the indicator 428 is a “1” or “on”, the processor 312 keeps the relay 316 closed 430. If the indicator is a “0” or “off”, the processor opens 432 the relay 316. The processor 312 then waits 434 for some period of time before continuing, such as 1 minute.

The system discussed above could operate in alternate embodiments such as rather than having a storage or memory that stores on/off indicators for time periods, a memory/storage could store on and off times and the system would determine if the current time was equal to or between the on/off times in an on or off period.

As depicted in FIG. 5, the temperature storage 510/314, rather than including essentially on/off indicators, can include set temperatures 512 for each of the time periods in which the water temperature is to be controlled, such as day, week, month or year. FIG. 5 shows a change in set temperature between the periods of 7:45 and 8:00 and between the periods 9:00 and 9:15, between the temperatures of 80 degrees F. and 140 degrees F., such as when a family might use hot water for bathing and breakfast on a weekday or weekend day. As can be seen, in this embodiment, the water temperature can be set for a desired temperature by the user. In this example of the storage 510, the time periods are 15 minutes each in length but could be other lengths such as 10 minutes or less and 30 minutes or more.

The system, in addition to the components as shown in FIG. 1, the temperature controller 610/318 (see FIG. 6) includes the temperature storage 612 and a processor 614/312 that is coupled to the temperature sensor 616/114.

As depicted in the process 710 of FIG. 7, when the input unit is activated 712, the system determines whether the function for setting the temperature for the time periods has been selected 714. If so, the user is allowed to enter 716 the start and stop time for a setting and the temperature that is to be set during that period. The set temperature for the time period is stored 718. In the example of FIG. 5, the user would enter the start and stop time periods of 8:00 and 8:45 and the temperature of 140. The system stores the set temperature in the temperature storage for each of the time periods in that range, that is, the time periods of 8:00, 8:15, 8:30 and 8:45. If no more temperatures are to be set 720, the system begins to control the water temperature. The current time is obtained 722 and the temperature storage for the time is accessed 724 to obtain the set temperature for the current time. The current temperature as determined by the sensor is obtained and compared 726 to the set temperature. If the current temperature is greater than or equal to the set temperature, the heating controller is turned off 728. If the current temperature is less than the set temperature, the heat controller is turned on 730. The system then waits 732 for a period of time before continuing.

In another embodiment of the system 810, including FIGS. 1, 5, 8 and 9, the temperature controller 812/610 (see FIG. 8) includes a set temperature storage 814 storing a set temperature which is accessed by a controller 816 which controls the heat controller 818/118 relative to the set temperature. A temperature management unit includes a processor 822 and the temperature storage 824 (see FIG. 5) that stores the varying temperature settings. The temperature storage 824 of FIG. 8 is accessed by the processor 822 and the processor 822 loads a temperature setting from the temperature storage into the set temperature storage 814 of the temperature controller 812 where the controller 812 controls the water temperature according to the set temperature in the set temperature storage 814 responsive to the sensor 826/114.

As depicted by the process 910 in FIG. 9, during operation, the processor 822 (see FIG. 8), obtains the current time 912 and then accesses 914 the temperature storage for the time period of the current time. The set temperature for that time period from the temperature storage is obtained and loaded 916 into the set temperature storage 814 of the temperature controller 816. The temperature controller then controls the heating controller based on the temperature loaded into the set temperature storage. The system then waits 918 for a period of time before continuing.

The embodiment discussed above could also operate in different ways. For example, rather than store a set temperature for each different period, the system could store triplets of on times, off times and temperature settings. The system would then determine a set temperature or the on/off of a heating unit by comparing and the using the triplets to control the heating of the water, such as setting a corresponding set temperature into the set temperature storage of the temperature storage when the current time is equal or between the on/off times of that temperature setting. The system could also include a pair of set time and temperature setting and when the current time equals the set time, the temperature setting could be loaded into the set temperature storage of the temperature controller.

A further embodiment of a heating process 1010 including FIGS. 1, 5, 6 or 8 and 10, determines when to start heating the water to ensure that a desired set temperature, such as 140 degrees is reached by a set time, such as 8:00, as depicted in FIG. 5.

For a natural gas water heater, natural gas contains about 1 therm (th) of heat per 100 cubic feet of gas which is 100 k BTU (British Thermal Units). The BTU of gas required to raise the temperature in a gas water heater from a current temperature to a target temperature is about:

gas BTU=gallon cap.*8.3 lbs/gal*(target temp.−current temp.)/100000

If we assume 40 gallon capacity water heater, a target temp of 105 degrees Fahrenheit (° F.), a current temperature of 55° F., the BTUs required to raise the temperature from the current temperature to the target temperature would be would be about:

0.166=40*8.3*(105/55)/100000

The time required is:

time required (hrs.)=gas BTU*100000/heat rate (BTU/hr. of water heater)

If we assume a heating rate of 40,000 Btu (40 k) per hour, the time required to go from 55 degrees to 105 degrees would be:

0.415=0.166*100000/40000

That is, it takes about 0.415 hours or approximately 25 minutes.

With a 30 gallon capacity gas water heater having a burner producing 20 k BTU, the time require is 0.625 hours or approximately 38 minutes.

In determining whether to start the burner of a natural gas water heater a determination such as set forth below can be made.

start (yes if negative)=time of demand−current time−time required

That is if the time of the demand minus the current time minus the time required is negative, the burner should be turned on. For example, using the 30 gallon example and 105 to 55 degree example noted above, if the demand time is 8:00, current time is 7:00 and the time required is 38 minutes (0.63 hrs), then 8−7−0.63=0.37 and the burner does not need to be started. However, if the current time is 7:30, then 8.0−7.5−0.63=−0.17 and the burner is to be turned on. That is, with the time being required as 38 minutes, at 7:22 (or 38 minutes before the demand time of 8:00 or 8−0.63=7.37 or 7:22) the burner needs to be turned on.

For an electric hot water heater:

BTU=watts*3.412

If we assume a water heater with an electric heating element capable of producing 4500 watts, the time (a tank temperature time) required for a 40 gallon electric water heater to raise the temperature from 55 to 105 is 1.08 hours or approximately 65 minutes. For a 30 gallon electric heater with an element producing 3 k watts, the time required would be 1.21 hours or about 73 minutes.

In this embodiment, as depicted in FIG. 10, the system obtains 1012 the current time and temperature and then accesses 1014 the temperature storage for the next temperature change and the time at which that temperature change is to occur. For example, in FIG. 5 when the current time is 7:30 the next temperature change occurs at 8:00 and the temperature rises to 140 from 80 degrees Fahrenheit.

The system then determines 1016 whether heating of the water in the tank is to be started as discussed above.

If not, the system waits 1018 until proceeding. This wait time needs to be some period, such as one minute, that will allow variations in the start time to be detected as hot water demand changes.

If heating of the water is to be started, the set temperature of the change is loaded 1020 into the set temperature storage or the heating element, thorough the heat control, is turned on.

The above discussed embodiment can also operate in other ways, for example, rather than storing temperatures for time periods as depicted in FIG. 5, the system can store triplets or pairs as previously discussed and the system determines from the temperature settings and the times whether to start heating the water as discussed above.

Another embodiment of a water heater 1110 is shown in FIGS. 5, 6 or 8, 11, 12 and 13. In this embodiment a water flow device 1112, such as a digital water flow meter, (see FIG. 11) is provided on the water intake or the hot water out flow pipe 1111 as shown. This meter 1112 records the water demand for periods of time over a desired period, such as a day, week, month or year.

The actual demand is recorded in a demand storage 1210, such as depicted in FIG. 12 which shows actual demand for a one and one-quarter hour period over the last 7 days in increments or periods 1212 of one-quarter hour. As can be seen the average demand in the 8:00 (am) period is about 20 gallons while the average demand in the 8:15 period is about 1 gallon. For each new day, the actual demand is preferably recorded over the demand in the storage so that a running moving average can be determined. For example, when Sunday arrives the demand for that day at the 8:00 period replaces the 21 gallon value in the storage 1210 and the system, using sensor 1118, controls controller 1120.

During operation of this embodiment, the time (a demand temperature time) required to raise the average demand water entering the water heater from the intake temperature to the set temperature is determined. For example, as depicted in FIG. 5 if the set temperature is 140 degrees F. at 8:00 on Tuesday, as depicted in FIG. 12, the average demand for that period is 20 gallons and the typical intake temperature for water coming from an underground water pipe entering a residence is about 60 degree F. As previously discussed the time required for a gas or electric water heater to raise the temperature of 20.5 gallons of water from 60 degrees to 140 degrees F. can be determined. The current temperature of the water in the tank can be used to determine the amount of time required to raise the tank temperature to the desired temperature. This time can then be used to determine whether the heating unit needs to be turned on as previously discussed

Note an intake water temperature sensor can be used to measure the actual temperature of water flowing into the water heater rather than assuming that the intake temperature is approximately the temperature of water entering the residence from and underground pipe and this case be used to determine the time to start reheating.

This embodiment can also determine the amount of time required to raise the entire tank of water from its current temperature to the set temperature. This tank temperature time and the demand temperature time can be combined to determine when to turn on the heating element.

As shown in the process 1310 of FIG. 13, the system obtains 1312 the current temperature from the temperature sensor and obtains the current time.

The temperature storage of FIG. 5 is accessed and the demand storage of FIG. 12 is accessed 1314 to obtain any change in set temperature and the future demand.

The demand temperature time and the tank temperature time are calculated 1316 and combined and used to determine whether the heating element is to be on.

If so, the set temperature is loaded 1318 into the temperature storage of the temperature controller. The system then waits 1320 for a period, such as one minute, before continuing.

For example, if we assume that we have a 40 gallon natural gas water heater with a heat rate of 40k BTU per hour, a current set temperature of 80 degrees, a future set temperature of 140 degrees F., a tank water temperature of 100, degrees F., an intake temperature of 60 degrees F. and a future demand of 20 gallons, the time before the set temperature and the demand which to start the heating of the water is to ensure a tank of water at the desired temperature about:

time=(((40*8.3*(140−100)/100000))+(20*8.3*(140−60)/100000)))*100000/40000

The above discussed embodiment can also operate in other ways, for example, rather than storing temperatures and demand for time periods, the system can store triplets or pairs of set times and temperatures and sets of times and demand values and the system determines from the temperature settings and the times whether to start heating the water as discussed above.

In another process 1410 embodiment, see FIG. 14, the stored demand can be used to determine whether to start or continue heating the water. In this embodiment the user has set a desired temperature for hot water provided during periods of demand, such as 140 degrees and a default temperature or a non-demand lower temperature setting, such as 80 degrees F. is used during periods of low or no demand.

In this approach 1410, as depicted in FIG. 14, the system obtains 1412 the current time and temperature (and the demand and no-demand temperatures) from the sensors and time clock.

The demand storage of FIG. 12 is accessed 1414 to obtain the current and future demand.

With the current water temperature, the demand temperature setting, and the demand from the demand storage, the system (see FIG. 14) determines 1416 whether it is a time when the heating element needs to be on using one of the approaches previously discussed.

If the water needs to be heated, the demand temperature is loaded 1418 into the set temperature storage or the heating element is turned on.

If the water does not need to be heated, the non-demand or off-peak temperature setting is loaded 1420. The system then waits 1422 for a period, such as one minute, before continuing.

In another 1510 embodiment (see FIG. 15) the current actual demand can be used to determine whether to essentially override a lower user setting to provide heated water when in a user lower setting period. In a typical off-peak period when there is low or no demand, demand for hot water can occur. For, example, a user might need to wash their hands, wash a single pot, start washing a load of cloths or start a dishwasher that has unexpectedly become full. When the activity is washing hands, it is likely that no water needs to be heated, because the demand is relatively low, say less than one gallon. However, when the demand is greater it is possible water may need to be heated to the users demand temperature.

In this embodiment 1510, the system reads 1512 the flow meter to determine whether there is any demand or flow (see FIG. 15). This can be determined in a number of different ways, such as by comparing a previous reading with a current reading.

If there is a detected demand 1514, the system begins monitoring 1516 the demand, which can be performed in a number of different ways. One approach involves taking a demand reading after a period of time, such a one minute. This reading is compared to a prior reading and any difference added to any previously stored demand reading.

To determine whether to start heating the water demand is compared 1518 to a demand threshold, such as the one gallon previously discussed.

If the demand is above the threshold, the system determines 1520 whether water heating needs to occur in one of the approaches previously discussed.

If so, water heating is started 1522 or continued to raise the temperature to the demand period temperature and demand monitoring is continued.

If the demand is not above the threshold, the system checks 1524 to see if the demand has stopped, such as when a current flow reading is the same as the previous flow reading.

The system then stores 1526 the accumulated demand and then, if in an off-peak period, sets 1528 the temperature to the off peak value.

The system then waits 1530 a period, such as one minute. After the period, the system determines 1532 if the stored demand needs to be reset 1534 to zero. For example, if there has been no demand for some period of time, such as an hour, the accumulated demand is reset to zero.

Another embodiment, as depicted in FIG. 16, can include two tanks 1610 and 1612 in the water heater 1614 with corresponding heat controllers 1616 and 1618 that are controlled by a temperature controller 1620. In this embodiment, the lower tank 1610 is kept at a lower temperature, such as 80 degrees F. and the upper tank is kept at the set temperatures set by the user. The system operates to control the temperature of the upper tank 1612 as in the embodiments discussed previously. Another approach is to set the lower tank temperature at some lower offset relative to the upper tank, such as 30 degrees F. less than the setting of the upper tank 1612 and the two tank temperatures are controlled using one of the control approaches as previously discussed. More than two tanks could also be used.

Demand has been discussed as being determined by water flow into or out of the water heater. However, the length of time that the heating element is turned on can also be used to measure demand. A water heater set at a desired temperature setting, such as 105 degrees F., actually fluctuates between the temperature setting where the heating element is turned off and a lower offset temperature, such as 100 degrees F., where the heating element is turned on.

A typical water heater is located in a residence in a site, such as a basement or storage room, having a relatively constant temperature, such as 70 degrees F. In such an environment, the rate at which the temperature declines from the desired set temperature to the offset temperature is governed by the heat loss from the water into the 70 degree F. environment. The loss time required for this decline is relatively stable. Likewise, the recovery time required for the heating element to bring the temperature up from the offset temperature to the desired temperature setting is also relatively constant and repeats throughout a low demand period as the water heater is “maintained” at the desired set temperature.

Temperature can also be used to control when the water heater is on or off for energy savings. In a temperature embodiment, a learning period, such as one or two weeks, can be used during which the system learns the water use habits by comparing the temperature to a threshold. As a larger amount of water is used (or demanded), such as when taking a bath the temperature of the water in the tank drops more than when hot water is used for a short or low demand period, such as when hand washing. The typical temperature drop in a short time period or some temperature below that by a few degrees can be used as the threshold. When the temperature drops below that threshold and then rises back above that threshold that period can be used to define a period of heavy use during which the water heater needs to remain on. At other times the temperature of the water can be allowed to continue to fall until heat needs to be applied to bring the temperature back up to the normal setting at the start of a heavy use period. One approach or process 1710 to determining these periods is depicted in FIG. 17. A temperature of the water measured by a temperature sensor is read 1712 and compared 1714 to the threshold. If the temperature is at or above the threshold, the system loops back to take another reading. This loop back can be controlled by a wait period 1716 that divides the learning period up into a number of periods, such as 15 minute periods. If the measured temperature is below the threshold, the system can store 1718, in a memory table (such as a PROM), the temperature and/or an indicator that the threshold has been crossed and that the heater is in a heavy use period. The system then determines 1720 whether the end of the learning period has been reached. If not, the system loops back for another temperature reading. If so, the learning period ends 1722 and the system starts operation to heat water during the use periods and not during non-use periods as previously discussed.

This recovery time of the water heater for the recovery demand can be measured outside of the residence and assumed as a standard or measured in the residence. This recovery time can be used to determine whether there is actual demand for heated water. For example, if the time that the heating element is on is longer than this recovery time, the demand is actual user demand and not recovery demand. By measuring the time period that the heating element is on that is longer than the recovery time along with the actual time at which the heating period exceeds the recovery time, the time of day (day, week, month and year) of a demand period and the length of demand period can be determined. Such determined demand periods can be used to fill a table such as in FIG. 12.

The description previously provided discusses a system that uses the current heat controller of a water heater. This controller could be eliminated and a processor with a temperature sensor could be used to control the water heating by activating the heating element or unit directly, allowing a user to set a desired temperature that would be maintained with an offset during demand periods and allowing the temperature in the tank to fall during non-demand periods.

The system also works with smart grid, peak demand control systems that are operated by utilities to turn off appliances during peak electricity demand periods using a load control switch. A load control switch is a remotely controlled that is placed on home appliances which consume large amounts of electricity, such as and electric water heaters. Load control switches typically include a communication module and a relay switch. The load control switch operates similarly to a pager to receive a control signal from the power company to turn off or reduce power to the appliance during times of peak electrical demand. The device also can have a timer that will automatically reset the switch back on after a preset time. The embodiments discussed herein can be used to override or interrupt the control signal or produce a reset signal when demand occurs and the heating element is off because in an low demand period and/or in a peak demand period. 

1. A water heating system, comprising: a water tank having a volume; a heating element adapted to heat the water in the tank and having a heating rate; a temperature controller having a temperature sensor and a temperature setting device adapted to control water temperature responsive to a user set temperature; and a demand controller adapted to control the temperature controller responsive to demand for heated water, the demand controller comprising: a water flow sensor adapted to sense an amount of water flow through the tank; an intake temperature sensor adapted to measure the intake water temperature; a current temperature sensor adapted to sense a current water temperature; a set temperature memory adapted to store the user set temperature; a intake temperature memory adapted to store the intake water temperature; a demand table memory adapted to store the water flow information for periods of time over the recurring period comprising periods during a day and days of a week; a current temperature memory adapted to store the current water temperature; a processor adapted to store the user set temperature when set by the user, adapted to periodically read and store the water intake temperature; adapted to read water flow sensed by the water flow sensor to store and update water demand information for the water flow over a recurring period of time adapted to periodically read and store the current water temperature, adapted to determine when the current time is within the demand period and to allow the temperature controller to control water temperature to the user set temperature during the demand period, adapted to determine when the current time is within a non-demand period to disable the temperature controller during the non-demand, adapted to determine when water heating is to start during the non-demand period to raise the current water temperature to the user set temperature at the start of a next demand period responsive to the current water temperature, the user set temperature, the volume and the heating rate.
 2. A water heating system, comprising: a water tank having a volume; a heating element adapted to heat the water in the tank and having a heating rate; a temperature controller having a temperature sensor and a temperature setting device adapted to control water temperature responsive to a user set temperature; and a demand controller adapted to control the temperature controller responsive to demand for heated water.
 3. A system as recited in claim 2, wherein the demand is determined by a user setting of on/off heating periods.
 4. A system as recited in claim 2, wherein the demand is determined by water flow.
 5. A system as recited in claim 4, wherein demand periods of the demand are periods of a day and days of a week.
 6. A system as recited in claim 5, wherein the demand periods comprise periods when flow is above a threshold.
 7. A system as recited in claim 6, wherein periods of demand change over time based on changes in water flow.
 8. A system as recited in claim 2, wherein demand periods of the demand are determined by water temperature.
 9. As system as recited in claim 7, wherein the demand periods comprise periods when water temperature is below a threshold.
 10. As system as recited in claim 2, wherein the demand controller starts temperature recovery to the set temperature in a non-demand period before a demand period.
 11. A water temperature control method for a water heater, comprising: setting a set temperature for water temperature of water in the water heater; determining demand periods and non-demand periods for use of hot water; and overriding the set temperature during non-demand periods. 